#A = (5, 2)#
#r: y = 2 - 1/4 x#
#s ⊥ r Rightarrow s : y = a + 4x#
#A in s Rightarrow 2 = a + 4 * 5 Rightarrow a = -18#
#s cap r = M: 2 - 1/4 x = -18 + 4x# // this is cohordinate x of M
#8 - x = -72 + 16x Rightarrow 80 = 17x#
#M = (80/17, 2 - 20/17) = (A + B)/2# // middle point of A and B
#80/17 = (5 + x)/2 and 14/17 = (2 + y)/2# // cohordinates of B
#160 = 85 + 17x and 28 = 34 + 17y#
#75 = 17x and -6 = 17y#